Investigations underway in the laboratory focus on the unique mechanisms of activation of T and B lymphocytes and how these cells interrelate in cellular immune responses. The demonstration that B lymphocytes in addition to T cells can liberate lymphokines which are the mediators of cellular immune responses implicated B cells as coparticipants in these reactions. However, the inability of these B cells to respond to antigen directly resulted in our identification of a T cell mediator which can recruit B cells into lymphokine production. Once triggered, these lymphocytes proliferate and produce biologically active lymphokines, some of which set on macrophages to initiate migration (chemotactic factor) and enzyme production (macrophage activation factor). Whether these and other signals for macrophage activation are translated via alterations in cyclic AMP and GMP levels is being investigated. In addition to lymphokines which trigger macrophage function, activated lymphocytes also release a soluble factor which stimulates fibroblast proliferation and modulates collagen synthesis. By this mechanism the immune system may control connective tissue metabolism in inflammatory lesions. BIBLIOGRAPHIC REFERENCES: Wahl, S. M. and Rosenstreich, D. L.: Role of B lymphocytes in cell-mediated immunity. I. Requirement for T cells or T cell products for antigen-induced B cell activation. J. Exp. Med. 144: 1175, 1976. Rosenstreich, D. L. and Wahl, S. M.: Cellular sources of lymphokines-lymphoid cells. In Oppenheim, J. J. and Cohen, S. (Eds.): Biology of the Lymphokines. Academic Press, N.Y. 1977 (in press).